There are a number of situations in which it is desirable to have a method of detecting movement of a closure for an opening in a structure out of its closed position. Such situations involve various types of structures. One example is an occupied dwelling, such as a room in a hotel or a home with opening doors and windows. In this example, an alarm device can serve to alert occupants of the unauthorized entry of an intruder through a door or window.
Another example is a storage area, such as a cabinet or drawer, where articles that may be dangerous to children are kept in a home or other facility where children are present. In this type of situation, it is desirable to prevent access by children to the storage area or, failing prevention of access, to immediately alert an adult that a child has gained access. The alerting of an adult can avert tragedy when a storage area is not locked or, as sometimes happens, an allegedly childproof lock is opened by a child.
Although the basic goal of signaling that undesired access to a structure has been gained is the same in both of the two types of situations described above, the two situations present different sets of problems. In the case of unauthorized access by an intruder into an occupied structure, the alarm device is most commonly associated with an inwardly opening closure, such as a door. In addition, the person to be alerted is inside the structure. In the case of storage areas the closure is normally opened outwardly, and the person to be alerted is outside the structure. Since the person is outside the structure, the alarm cannot be set from inside the structure.
The patent literature includes a number of examples of portable burglar alarms for use especially by travelers staying in hotel rooms. The patents include U.S. Pat. Nos. 1,099,777, granted Jun. 9, 1914, to S. Sundel; No. 1,562,574, granted Nov. 24, 1925, to G. J. Maud; No. 2,259,696, granted Oct. 21, 1941, to C. P. Hulst; No. 3,932,856, granted Jan. 13, 1976, to Leo J. Tremont; No. 4,264,899, granted Apr. 28, 1981, to John I. Menzies et al.; No. 4,438,428, granted Mar. 20, 1984, to John W. Ober et al.; and No. 4,808,974, granted Feb. 28, 1989, to Richard E. Cantley. Each of the alarms disclosed in these patents is designed to be set by the room occupant from inside the room and to be used with an inwardly opening door. The device disclosed by Tremont may also be used with an outwardly opening door. The Sundel device is attached to the door and is operated by a chain which engages a lever. The Maud, Hulst, Tremont, and Menzies et al. devices are placed on the floor by the door and are operated by movement of the door causing movement of all or part of the device. The Tremont device may also be operated by a string or by a gravity operated lever when the device is used with an outwardly opening door. Each of the Ober et al. and Cantley devices is mounted on the door and has a lever that projects upwardly from the device and is biased to pivot into a position in which it projects rearwardly from the device. The device is hooked onto the top of the door with the lever positioned against the door frame to stop rotation of the lever.